Forging of workpieces

ABSTRACT

The invention relates to apparatus for enlarging part of a metal workpiece by cold forging, characterised by an enlarging die ( 5, 6 ) and by the die having means ( 8, 8′ ) to alleviate stress to the workpiece during forging.

[0001] The invention relates to forging of workpieces, particularlymetal workpieces such as reinforcing bars for use in buildingconstruction, particularly concrete construction.

[0002] Concrete reinforcing bars, which may be deformed by externalribs, or plain, are usually provided in finite lengths.

[0003] It is often necessary to join them in line to provide a moreextensive reinforcement than might otherwise be possible owing to thefinite length. Such bars have a high tensile strength, and it isaccordingly necessary not to undermine that strength during any processto enable the bar to be connected with another. Usually this is effectedby providing a thread on one end, usually by cold working, which can beadvantageous as the bars are usually made from steel with a high carbonand manganese content. However, forming a thread at one end of the baroften reduces the cross-section of the bar, thus lowering its tensilecross-section in the region of the thread, which leads to failure inuse, which can be catastrophic for the concrete. It is thus necessary toensure that the threaded end (which is formed by rolling, milling orcutting) is enlarged, relative to the remaining length of the bar, sothat the effective tension cross-section of the threaded part is notsmaller than that of the remaining length of bar. However, in the past,enlarging techniques have not been able satisfactorily to produce anenlarged end of a ribbed bar in which the tensile strength is noteffected as compared with that of the remainder of the bar.

[0004] It is an object of the invention to seek to mitigate thesedisadvantages.

[0005] According to a first aspect of the invention there is providedapparatus for cold forging a metal workpiece, comprising a die withmeans to alleviate stress to the workpiece during forging.

[0006] According to a second aspect of the invention there is providedapparatus for enlarging part of a metal workpiece by cold forging,comprising an enlarging die with means to alleviate stress to theworkpiece during forging.

[0007] Using the invention it is possible to provide an enlarged end ofdeformed (ribbed) and undeformed reinforcement bars without changingtheir overall tensile characteristics.

[0008] The stress alleviating means may comprise a relief channel intowhich metal can flow during forging. This is a relatively simple yeteffective construction, particularly where the relief channel may be asubstantially U-shaped groove in the die.

[0009] There may be two opposed dies. This provides for positiveenlargement over the whole circumference of the workpiece.

[0010] Each die may have a first die part and a second die part whichsecond die part may be enlarged relative to the first die part and maybe adapted to allow part of the workpiece to project therefrom, thearrangement being such that in use the projecting part of the workpieceis upset and enlarged. This is a particularly simple and efficientconstruction.

[0011] There may be means to press the die parts together, and means toapply pressure in a direction substantially at 90° to thefirst-mentioned press direction. This provides for maintaining a tensileintegrity of the workpiece during a forging/enlarging procedure.

[0012] The means for pressing the die parts together may comprise anhydraulic press acting substantially vertically in use. This is aneffective construction.

[0013] The second-mentioned means may comprise an hydraulic press actingsubstantially horizontally. This is also an effective construction.

[0014] At least the distance between the enlarging die and thesubstantially-horizontally acting hydraulic press may be adjustable.This provides for a desired enlarging operation.

[0015] The distance may be adjustable by adjusting the pressure of aforging piston for effecting forging. This is an effective way ofadjusting the operation.

[0016] An equally effective alternative may be by the distance beingadjustable by adjustment of a forging pad on which the forging pistoncan act.

[0017] The pressure of the substantially vertically acting hydraulicpress may also be adjustable. This again provides a desired control ofthe procedure.

[0018] The first die part may have an internal die configurationsubstantially complementary to the external configuration of a majorpart of a workpiece which is to be forged. This provides for support ofthe workpiece during enlargement.

[0019] According to a third aspect of the invention there is provided amethod of cold forging an elongate metal workpiece, comprising the stepsof providing forging apparatus having a die, providing the die withmeans to alleviate stress in the workpiece during forging, and forgingthe workpiece.

[0020] The method may include the steps of providing two opposed forgingdies. This provides a positive method of operation.

[0021] Each forging die may comprise a relief channel into whichmaterial of the workpiece can flow during forging. This provides thatthe tensile integrity of the workpiece is maintained.

[0022] There may be the steps of providing that each die part has afirst die part and a second die part enlarged with respect to the firstdie part, inserting an elongate workpiece between the dies so that thefirst die part receives a main part of the workpiece, and an end of theworkpiece projects through and beyond the second die part, and upsettingthe projecting end so that it flows into the enlarged second die part.This provides an efficient method of enlargement.

[0023] There may be the steps of removing the forged workpiece from theapparatus and forming a thread on the enlarged part of the workpiece.This provides a way to connect the workpiece with another similar one.

[0024] According to a fourth aspect of the invention there is providedan elongate metal workpiece whenever forged by a method as hereinbeforedefined, or whenever produced by a method as hereinbefore defined.

[0025] The elongate metal workpiece may have at least one threaded end,and may comprise a reinforcing bar for use in building construction.

[0026] Such a reinforcing bar may have an internally threaded sleeve onan end opposite an enlarged threaded end.

[0027] According to a fifth aspect of the invention there is provided areinforcing system, comprising a plurality of reinforcing bars ashereinbefore defined.

[0028] According to a sixth aspect of the invention there is providedconcrete whenever reinforced by a workpiece or reinforcing bar ashereinbefore defined.

[0029] Apparatus and a method for cold forging or enlarging a metalworkpiece by cold forging is hereinafter described, by way of example,with reference to the accompanying drawings.

[0030]FIG. 1 shows a copy of a photograph of the threaded end of a priorart deformed metal reinforcing bar for use in reinforcing concrete inbuilding construction;

[0031]FIG. 2 shows a cross-section at ‘b’ in FIG. 1;

[0032]FIG. 3 shows an enlargement of C in FIG. 2, at a magnification of20:1;

[0033]FIGS. 4 and 5 show respectively schematic elevational views ofapparatus according to the invention for soft-cold forging/enlarging ofa metal reinforcing bar;

[0034]FIGS. 6 and 7 show an end elevational view of forging dies used inthe apparatus of FIGS. 4 and 5, FIG. 6 showing a reinforcing bar inposition;

[0035]FIG. 8 shows a side elevational view of the forging dies of FIG. 6with the reinforcing bar in position for enlargement of one end;

[0036] FIGS. 9 to 11 show stages in the production of an enlargedthreaded end of a reinforcing bar according to the invention;

[0037]FIG. 12 shows use of a reinforcing bar according to the invention;and

[0038]FIG. 13 shows a reinforcement system comprising a plurality ofreinforcing bars according to the invention.

[0039] Referring to the drawings, there is shown apparatus 1 (FIGS. 4 to8) for cold forging or enlarging a metal workpiece in the form of areinforcing bar or rebar 2 for concrete comprising a die 3 to alleviatestress to the workpiece 2 during forging.

[0040] Thus a reinforcing bar 2 with a very high tensile strength whichhas a variable outer configuration owing to the variation in the sizeand shape of surface deformations (ribs), particularly longitudinallyextending ones 4 can be soft cold enlarged without reducing themechanical characteristics and strength of the reinforcing bar 2. Thusthe tensile strength and yield strength of the reinforcing bars are notreduced, unlike in the prior art of FIGS. 1 to 3. FIG. 1 shows an end ofa prior art reinforcing bar A which has been enlarged and then had athread ‘T’ applied to it. There is a tendency for a crack ‘C’ to form,FIGS. 2, 3, if the enlarging process is not controlled so that theenlargement is either too large or conversely too small. In this lattercase, the failure occurs at the threaded section as the cross-sectionalarea of the thread is too small. Such dimensional irregularities willlead to early failure in use of the prior art rebar A.

[0041] This is obviated using the apparatus 1 of FIGS. 4 to 8, in whichthere is the die 3 in the form of a pair of substantially vertically (asviewed) opposed dies 5, 6, each having a guide channel or track 7 forlongitudinal ribs 4 of the rebar 2, each die also having a relief stressalleviating means in the form of a substantially U-shaped groove 8′which extends from a second die part 8 or enlarging die which isenlarged with respect to a first die part 9. There is also a taperedtransition or contour 10 between the first and second die parts 9, 8which allows a controlled application of pressure.

[0042] The first die part 9 is complementary to the outer diameter ofthe main body part of the reinforcing bar 2. The length of the dies 5, 6is such that the reinforcing bar 2 at one end extends through and beyondthe enlarged die part 8. The apparatus 1 includes a first pressureapplying means in the form of an hydraulic press 11 which actssubstantially vertically (as viewed) to act on the main part of thereinforcing bar by pressing on the ribs 4. This reduces the risk ofincreasing stress in the reinforcing bar 2 during enlargement of theend. There is also a second pressure applying means in the form of anhydraulic press 12 which acts substantially horizontally (as viewed).The horizontal distance can be adjusted as desired by adjusting thedistance of the piston 13 and/or by adjusting a pad or disc 14 which pador disc 14 is intermediate the piston 13 and the enlarged die part 8.The effect is to adjust the distance of the reinforcing bar whichprojects beyond the enlarged die part 8. Other means of adjustment maybe utilised.

[0043] In operation to form an enlarged end 2 a of the reinforcing bar2, the dies 5, 6 are separated vertically, the reinforcing bar 2 isinserted through a guide and support 15 in a frame 16 of the apparatus1, so that the end to be enlarged projects beyond the enlarged die parts8. The bar 2 is then gripped by lowering the die part 5 vertically,arrow ‘X’ via its piston 17 to engage the lower die part so that the bar2 is supported over substantially the whole length of its main body.Then the hydraulic press 12 is actuated to act on the projecting end toupset it in a cold forging operation, the relief groove 8′ allowing theupsetting to take place without the imposition of additional stressesduring enlargement. Also, the groove 8′ allows the shape and dimensionsto be controlled in a positive manner which control is assisted by thetapered zone 10, which with the relief groove 8′ allows a smooth,controlled enlargement with alleviation of stress build up, so that thebar has a tapered part 17 between the main body and the enlarged end 2 awith no additional stresses.

[0044] After enlargement of one end, the other end can be enlarged too,or not. The enlarged end(s) is/are then threaded by rolling, milling orbroaching to form a thread 18. As the enlarging operation is effectedcold, with no increase in stress, the material of the enlarged end is“soft”, so facilitating a rapid thread-cutting operation without damageto the thread cutting tools. The provision of soft cold forging allowsfor stress relieving so that there is no increase in stress in theenlarged end, and the control of the distance of the projectingreinforcing bar beyond the enlarging dies 8 provides the desired propersize of the end being enlarged. Thus the enlarged end is not too large(which would create a crack in the enlarged end), and not too small(which would create failure in the thread region), according to theparticular size and shape of the reinforcing bar being enlarged.

[0045]FIG. 12 shows a reinforcing bar 2 with an internally threadedsleeve 19 on one end in concrete 20 about to be connected with areinforcing bar 2 according to the invention, the threaded enlarged end2 a, 18 being screwed into the sleeve 19 to effect connection. This canbe effected manually on site, with the aid if required of pliers ortongs. FIG. 13 shows a reinforcement for concrete in the form of acomplete system of reinforcing bars connected together—looking from theleft there is a bar 2′ with a sleeve 19 (like that of FIG. 12) a bar 2″with enlarged threaded ends, a bar 2″′ with a threaded sleeve 19 at eachend, a bar 2″″ with a threaded enlargement at one end and an internallythreaded sleeve 19 at the other, a bar 2 ⁵ with a double externalenlarged thread at each end, a sleeve 21 with internal threads at bothends and a bar 2⁶ with an enlarged threaded end. These, it will beunderstood, are examples of possible combinations for connectingreinforcing bars embodying the invention in a reinforcement system forconcrete.

[0046] It will be understood that the operation of the dies 5, 6 and ofthe press 12 is under the control of a power pack unit ‘P’ as shown inFIGS. 4, and 5 which is a numerically controlled unit.

[0047] Thus the timing of the pressing operation, and the pressurethereof can be controlled automatically. Thus the same pressure can beused for rebars of varying diameter e.g. 120 bar or 180 bar pressure maybe used, the apparatus 1 acting to upset the end of the rebar 2 beingcold-forged, whatever its diameter. This is achieved by a sensor 23which may be a mechanical trip switch, or other means such as a laser orother optical device which is placed adjacent the face 22 of the dies 5,6 facing the press 12 and which senses the approach of the piston 13 andpad 14 and actuates the press 12 to cease action and return to a startposition just before the piston 13/pad 14 contacts the facing face 22 ofthe dies 5, 6. On ceasing application of the pressure, nevertheless thematerial of the rebar continues to flow to finish finally forming theupset end. Thus the sensor 23 acts to ensure that there is no need toadjust the force applied whatever the diameter of the rebar being coldforged. The pressure on the die faces 22 would be about 340 bar if therewas contact with the piston 13/pad 14. With the sensor, the pressure isonly 120-180 bar, which therefore saves the dies 5, 6 from damage, timeis saved as no re-setting of pressure is required, power is saved, thereis less general wear and tear on the apparatus, and on personneloperating same.

[0048] Also, before a forging operation, the start position (to theright in FIGS. 4, 5) of the pad 13 is set to define the length of therebar 2 projecting to the right as viewed, beyond surfaces 22. This thusprovides a simple way of inserting the rebar in the apparatus so that itabuts the piston 13/pad 14 prior to forging.

[0049] In a general procedure, a user of rebars 2 of a particular lengthwhich are too short and requiring to be lengthened are sent to theapplicant, who forges and threads one end, and usually adds a sleeve tothe opposite end, and the modified rebar is then sent back to thecustomer, for use as shown in FIG. 12.

[0050] It will be understood too that the apparatus 1 described withreference to the drawings provides a regular and homogenous enlarged end2 a in which the stresses are virtually identical to those in theunenlarged part of the bar so that a full load can be applied when usedin concrete constructions. Moreover, cold enlarging as described hereinwith reference to the drawings is also advantageous in that it can becarried out at a desired location, e.g. a construction or job site, asthe apparatus can be mobile. Also, cold enlarging is less expensive thanhot enlarging as no heating energy is required, and no additional timeneed be allowed for heating up and cooling down of a workpiece.

1. Apparatus for cold forging a metal workpiece, characterised by a die(6) and by the die (5, 6) having means (8, 8′) to alleviate stress tothe workpiece during forging.
 2. Apparatus for enlarging part of a metalworkpiece by cold forging, characterised by an enlarging die (5, 6) andby the die having means (8, 8′) to alleviate stress to the workpieceduring forging.
 3. Apparatus according to claim 1 or claim 2,characterised by the stress alleviating means (8, 8′) comprising anenlarged die part into which metal can flow during forging.
 4. Apparatusaccording to claim 3, characterised by the enlarged die part comprisinga substantially U-shaped groove (8′) in the die (5, 6).
 5. Apparatusaccording to claim 3 or claim 4, characterised by there being twoopposed dies (5) and (6).
 6. Apparatus according to claim 5,characterised by each die (5, 6) having a first die part (9) and asecond die part (8) which second die part (8) is enlarged relative tothe first die part (9) to form the means (8′) and is adapted to allowpart of the workpiece to project therefrom, the arrangement being suchthat in use the projecting part of the workpiece is upset and enlarged.7. Apparatus according to claim 6, characterised by means (11) to pressthe die parts together, and by means (12) to apply pressure in adirection substantially at 90° to the first-mentioned press direction.8. Apparatus according to claim 7, characterised by the means (11) forpressing the die parts together comprising an hydraulic press actingsubstantially vertically in use.
 9. Apparatus according to claim 7 orclaim 8, characterised by the second-mentioned means (12) comprising anhydraulic press acting substantially horizontally.
 10. Apparatusaccording to claim 9, characterised by at least the distance between theenlarging die (5, 6) and the substantially-horizontally acting hydraulicpress (12) being adjustable.
 11. Apparatus according to claim 10,characterised by the distance being adjustable by adjusting the pressureof a forging piston (13) for effecting forging.
 12. Apparatus accordingto claim 11, characterised by the distance being adjustable byadjustment of a forging pad (14) on which the forging piston (13) canact.
 13. Apparatus according to any of claims 9 to 12, characterised bythe pressure of the substantially vertically acting hydraulic press (11)being adjustable.
 14. Apparatus according to any of claims 6 to 13,characterised by the first die part (9) having an internal dieconfiguration substantially complementary to the external configurationof a major part of a workpiece which is to be forged.
 15. A method ofcold forging an elongate metal workpiece, characterised by the steps ofproviding forging apparatus (1) having a die (5, 6), by providing thedie (5, 6) with means (8′) to alleviate stress in the workpiece duringforging, and by forging the workpiece.
 16. A method according to claim15, characterised by the method including the steps of providing twoopposed forging dies (5, 6).
 17. A method according to claim 16,characterised by each forging die (5, 6) comprising a relief channel forreceiving a rib of a workpiece (2).
 18. A method according to claim 17,characterised by including the steps of providing that each die part (5,6) has a first die part (9) and a second die part (8) enlarged withrespect to the first die part (9), inserting an elongate workpiece (2)between the dies (5, 6) so that the first die part receives a main partof the workpiece (2), and by an end of the workpiece projecting throughand beyond the second die part (8), and by upsetting the projecting endso that it flows into the enlarged second die part (8′).
 19. A methodaccording to claim 18, characterised by including the steps of removingthe forged workpiece (2) from the apparatus and forming a thread on theenlarged part (2 a) of the workpiece (2).
 20. An elongate metalworkpiece whenever forged by apparatus according to any of claims 1 to14, or whenever produced by a method according to any of claims 15 to19.
 21. An elongate metal workpiece according to claim 20, characterisedby having at least one threaded end.
 22. An elongate metal workpieceaccording to claim 21, characterised by being reinforcing bar (2) foruse in building construction.
 23. A reinforcing bar according to claim22, characterised by having an internally threaded sleeve (19) on an endopposite an enlarged threaded end.
 24. A reinforcing system,characterised by a plurality of reinforcing bars (2) according to any ofclaims 22 or
 23. 25. Concrete whenever reinforced by a workpiece orreinforcing bar according to any of claims 22 to
 24. 26. A die for usein cold forging a metal workpiece, characterised by means (8′) toalleviate stress to the workpiece during forging.
 27. A die according toclaim 26, characterised by the means (8′) comprising an enlargedU-shaped groove part of a die (5) or (6).